Tubes are ubiquitous in industrial applications, with some common uses including supporting wind turbines (or other machinery) and transporting fluid. It is often desirable to vary thickness of one or more tubes formed for a particular application. For example, in large-scale industrial applications, such as formation of wind turbine towers, tubes used to form such towers are built in a factory setting and are limited to a maximum diameter constrained by transportation restrictions. With diameter of the tube constrained in this way, it is often desirable to vary wall thickness of the tube along the length of the tube to form the tube with desired structural performance characteristics. In particular, it is often desirable for the wall thickness to gradually increase along one direction in the tube (e.g., to accommodate the increasing moment loading along the axis of the tube, so that the thickness at one end of the tube is substantially greater than the thickness at the other end of the tube).
Variation of thickness of tubes, however, creates certain challenges with respect to efficient use of material and throughput in production processes used to form these tubes. As an example, transitions in thickness from one tube to the next may produce scrap, for example, when the change in thickness is too large to be accommodated by a continuous production process. This may occur, for example, at the transition between two instances of the same tube with gradually increasing wall thickness, with the first end having a substantially greater thickness than the second end. Further, if the tube is being formed using a continuous production process, the process may need to pause for the thickness change to be accommodated. For example, before the next tube can be formed, the scrap must be removed and additional steps taken to re-start the process. Production of scrap and slowing or pausing the continuous production process can both add significantly to the cost of a tube. Thus, there remains a need for improved methods of producing tubes having longitudinal variations in thickness.